1. Technical Field
The present invention relates to the field of optical devices and more particularly without limitation to beam splitters, optical switches and interferometric phase measurement devices.
2. Description of the Related Art
Some crystalline materials have different indices of refraction associated with different crystallographic directions. A common situation with mineral crystals is that there are two distinct indices of refraction depend on the polarization of the light traveling through the crystal; such crystals are called birefringent materials.
Typically birefringent materials are tourmaline, calcite, quartz, sodium nitrate, and rutile (Ti02). For example, the Wollaston prism makes use of the phenomenon of double refraction or birefringence, through which a crystal of a transparent anisotropic material refracts orthogonally polarized light beams at different angles. Birefringent crystals such as calcite, quartz, and mica are used for fabrication of such prisms:
For example the Wollaston prism includes two wedge-shaped segments held together with adjacent polished surfaces extending along a plane at an oblique angle to the optical axis of the device. The outer surfaces of the Wollaston prism lie along planes perpendicular to the geometrical-optical axis of the device. The two segments of the Wollaston prism are composed of a birefringent material, with the crystallographic-optical axes of the material lying perpendicular to each other and to the geometrical-optical axis of the device.
For example, if a beam of light consisting of two sub-beams polarized orthogonally to each other is directed along the geometrical-optical axis of the device to a Wollaston prism, the two beams will not be refracted at the initial surface of the prism, since it lies perpendicular to the direction of both beams. However, when the two beams reach the oblique inner surfaces of the two segments of the prism, refraction will occur, with the two beams being refracted at different angles because of the birefringence of the material of which the prism segments are composed. When the two beams reach the opposite external side of the prism, they are again refracted. U.S. Pat. No. 5,784,163 shows an interferometer, which uses such a Wollaston prism.